This products liability case involves a manufacturer’s duty to warn or instruct a user on the safe operation of a machine.
Petitioner, Louis Magro, Jr., sued Rags-dale Brothers, Inc., the manufacturer of a machine. The jury found all issues for the plaintiff Magro, and the trial judge rendered judgment on the verdict for Magro. The court of appeals reversed the judgment of the trial court and remanded the cause finding insufficient evidence to support the jury finding of producing cause. 693 S.W.2d 530. We reverse and render judgment affirming the trial court.
The plaintiff, Magro, was a foreman at the Pearl Container Corporation in San Antonio. He was trained to clean and maintain a can punch machine, called a “body-maker,” that was manufactured by Rags-dale Brothers. On May 16, 1980, Magro approached a continuously running body-maker, opened an access door which disengaged the motor, and extended his hand inside the bodymaker to clean the tool-pack area. Although the machine automatically stopped when the door was opened, it could be reactivated if someone at the control panel switched it into the “inch” mode. A co-worker of Magro, Calvin Sanders, turned the control to “inch” to enable him to clean another part of the machine. Mag-ro’s hand was caught in the bodymaker and severely mangled.
Magro’s suit alleged Ragsdale Brothers’ failure to warn or instruct him concerning the dangers of the bodymaker rendered the machine unreasonably dangerous. At trial, Peter Mandel, a Ragsdale Brothers design engineer, testified that no specific warnings or instructions were made available to Magro. Mandel also listed three instructions which could have made the machine safer. He stated that one working on the bodymaker should work alone, turn the machine off at the control panel with a key, and then remove the key from the control panel. Magro testified that he was performing his job as he had been taught and that he had not received any of Mandel’s suggested instructions at the time of the incident. Judd Clayton, an electrical design engineer, testified that the bodymaker’s foreseeable dangers made adequate warnings or instructions imperative for safe use. In his opinion the absence of warnings or instructions on the bodymaker’s control panel made the bodymaker unreasonably dangerous.
The jury found that Ragsdale Brothers failed to give adequate warnings or instructions for the safe use of the machine when it sold the bodymaker and that such a failure rendered the machine unreasonably dangerous. The court of appeals held the evidence on these issues to be legally and factually sufficient. The jury also found that Ragsdale Brothers’ failure to warn or instruct was the producing cause of Mag-ro’s injury. The court of appeals reversed *834and remanded the cause for a new trial holding the causation evidence factually insufficient.
Magro initially contends that he proved as a matter of law that Ragsdale Brothers’ failure to warn or instruct, which rendered the machine unreasonably dangerous, was a producing cause of his injuries. If so, the court of appeals’ insufficiency holding on that issue was erroneous.
An unreasonably dangerous product must be a producing cause of a plaintiff’s injuries to create liability.1 General Motors Corp. v. Hopkins, 548 S.W.2d 344, 351 (Tex.1977). Once a plaintiff proves the lack of adequate warnings or instructions rendered a product unreasonably dangerous, his producing cause burden is aided by the presumption described in Technical Chemical Co. v. Jacobs, 480 S.W.2d 602 (Tex.1972). When a manufacturer fails to give adequate warnings or instructions, a rebuttable presumption arises that the user would have read and heeded such warnings or instructions. Id. at 606; see also Restatement (Second) of Torts § 402a comment j (1965); Reyes v. Wyeth Laboratories, 498 F.2d 1264, 1281 (5th Cir.) cert. denied 419 U.S. 1096, 95 S.Ct. 687, 42 L.Ed.2d 688 (1974). This presumption may be rebutted with evidence that the user was blind, illiterate, intoxicated at the time of the product’s use, irresponsible, lax in judgment, or by some other circumstance tending to show that the improper use would have occurred regardless of the proposed warnings or instructions. Technical Chemical Co., 480 S.W.2d at 606.
The court of appeals correctly recognized that the Technical Chemical Co. presumption that warnings will be heeded should be applied when reviewing the sufficiency of causation evidence in this case; however, the court held that the presumption had been rebutted because Magro and Sanders exhibited “laxity in judgment.” The court found two instances of “laxity in judgment.” First, Sanders testified that he did not notice Magro working just two feet away before Sanders activated the body-maker. Second, Magro stated that he did not inform Sanders that he was working on the machine and did not see Sanders step to the controls.
The court of appeals’ interpretation of our Technical Chemical Co. “lax in judgment” rebuttal illustration is erroneous. The court apparently inferred, based on a single instance of inattentiveness, unrelated to reading or heeding safety information, that Magro and Sanders would not have paid attention to adequate warnings or instructions had they been given. This type of inference is impermissible. Evidence of inattentiveness, unrelated to the plaintiff’s ability to perceive or heed warnings or instructions and which does not rise to the level of habit under Tex.R.Evid. 406, is not admissible to prove that Magro and Sanders would have acted in a consistent manner by ignoring adequate warnings or instructions. Tex.R.Evid. 404.
A review of the record further reveals that there is no evidence to rebut the presumption in this case. Magro proved the absence of warnings or instructions rendered the bodymaker unreasonably dangerous and this finding is not challenged. Thus, it is presumed that Magro would have heeded adequate warnings or instructions by turning off the machine and removing the key before cleaning it. The “laxity in judgment” conduct which Rags-dale Brothers contends rebuts the presumption occurred after Magro began working. To be relevant, evidence to rebut the presumption must arise prior to the time that the plaintiff’s response to adequate warnings and instructions becomes presumed under Technical Chemical Co.
In addition to the presumption, considerable testimonial evidence supports the jury’s affirmative finding of producing *835cause. Magro testified that he always followed work related instructions and warnings and that he certainly wished he would have been told to work alone and take the key out when he turned off the machine. Judd Clayton, an expert witness, stated that adequate instructions and removal of the key would have prevented the accident. Ragsdale Brothers’ own expert, Mandel, also admitted that had his suggested instructions been given and followed, the incident probably would not have occurred. Because all of the testimony in this case supports the jury’s findings and no evidence rebuts the Technical Chemical Co. presumption, we hold that producing cause was established as a matter of law.
A second question is the suggestion by the court of appeals that the trial court submit an issue inquiring into misuse by both Magro and Sanders upon retrial of this cause. At the time of trial, the defense of unforeseeable product misuse had not yet been subsumed under the single issue of contributory negligence. General Motors Corp. v. Hopkins, 548 S.W.2d at 349. Between the time of trial and the decision on appeal, we decided Duncan v. Cessna, 665 S.W.2d 414 (Tex.1984). The court of appeals erroneously ordered the trial court to submit Sanders’ misuse as contributory negligence pursuant to Duncan even though Sanders is not a plaintiff in this case. Contributory negligence issues should only inquire into the conduct of a plaintiff. Id. at 428. Semantics aside, the court of appeals apparently believed that Sanders should be treated as a settling defendant under Duncan because Magro received workers’ compensation for his injuries.
The court of appeals did not discuss whether Sanders’ status as a co-employee prevents the submission of his negligence. Article 8306 § 32 of the Texas Workers’ Compensation Act abrogates an employee’s right to common law damages from his employer for personal injuries covered by the Act; however, a covered employee may seek recovery from a third party whose negligence or defective product contributed to the work related injury. In the event of recovery, the third party is barred from seeking contribution or indemnity from the employer or other employees.
In Varela v. American Petrofina Co., 658 S.W.2d 561 (Tex.1983), the issue before us was whether an employer’s negligence may be considered in a third party action brought by an employee arising out of an injury covered by workers’ compensation. We ruled that the legislature intended article 8306 § 3 to be an exception to the Texas comparative negligence statute, Tex.Rev. Civ.Stat.Ann. art. 2212a § 2b (now codified at Tex.Civ.Prac. and Rem.Code § 33.012 [Vernon 1986]). We held that a covered plaintiff’s third party negligence recovery will not be diminished by his employer’s negligence. Id. at 562.
Our Varela rationale is applicable and controlling in the present case. Duncan allows a defendant to have his liability for damages reduced by the causation percentage attributable to other settling defendants. We specifically held in Varela that an employer does not become a settling defendant under article 2212a § 2e simply because the plaintiff did not refuse workers’ compensation coverage during the first five days of his employment. Id. Likewise, a co-employee like Sanders does not become a settling defendant under Duncan just because Magro accepted workers’ compensation when beginning his employment.
*836The Duncan decision established a comparative causation scheme under which a non-settling defendant manufacturer can receive contribution from settling defendants. A plaintiffs recovery and a manufacturer’s liability are reduced by the percentage of causation attributable to a settling defendant’s negligence. Duncan, 665 S.W.2d at 432. The provisions of the Workers’ Compensation Act prevent Magro from having a right of recovery against Sanders. Since a defendant’s right of contribution is derived from a plaintiff’s right of recovery, Ragsdale Brothers has no claim for contribution against Sanders under Duncan. Varela, 658 S.W.2d at 563. Accordingly, we hold that a co-employee’s negligence should not be considered in a third party products liability action when the plaintiff’s injuries were covered by workers’ compensation.
The final question we address is whether the court of appeals correctly ruled that a requested “no duty to warn” instruction should have been given to the jury. Rags-dale Brothers requested the instruction but the trial court refused to submit it. The requested instruction read:
There is no duty to warn a group or class of users who possess special knowledge or expertise concerning the dangerous characteristics of the product.
Tex.R.Civ.P. 277 provides that the trial court shall submit such explanatory instructions and definitions as would be proper to enable the jury to render a verdict. A trial court’s refusal to submit requested instructions will not be overturned on appeal unless the court abused its discretion. Mobil Chemical Co. v. Bell, 517 S.W.2d 245, 256 (Tex.1974); DeLeon v. Otis Elevator Co., 610 S.W.2d 179,181 (Tex.Civ. App.—San Antonio 1980, writ ref’d n.r.e.). Here, the court of appeals recognized that the instruction refusal “may well” have been within the trial court’s discretion, but nevertheless suggested its submission upon retrial.
In the recent case of First International Bank v. Roper Corp., 686 S.W.2d 602, 604 (Tex.1985), we held that appropriate special issues ask the jury about the existence of a product defect and its causal connection to the accident. Any additional instructions serve merely to distract the jury’s attention from the essential issues of the case. Id. The trial court’s denial of the instruction here was a proper exercise of its discretion.
Since the court of appeals has already overruled Ragsdale Brothers’ other insufficiency points, we reverse the court of appeals judgment and render judgment affirming the trial court.
. The trial court in the present case defined producing cause as “an efficient, exciting, or contributing cause, which, in a natural sequence, produced the occurrence. There can be more than one producing cause.” 3 State Bar of Texas, Texas Pattern Jury Charges PJC 79.01 (1982).
. Tex.Rev.Civ.Stat.Ann. art. 8306 § 3 (Vernon’s Supp.1986) provides in pertinent part:
The employees of a subscriber ... shall have no right of action against their employer or against any agent, servant, or employee of said employer for damages for personal injuries ... but such employees ... shall look for compensation solely to the association.... If an action for damages on account of injury ... is brought by such employee ... against a person other than the subscriber ... and if such action results in a judgment against such other person, or results in a settlement by such other person, the subscriber, his agent, servant or employee, shall have no liability to reimburse or hold such other person harmless on such judgment or settlement.... No part of this Section is intended to lessen or alter the employees existing rights or cause of action ... against ... any third party.